Attach decimal part to an integer

Question

I need to be able to attach an integer number to another integer as a decimal part, for example:

For numbers 12345 and 12345678 I would want to get: 12345,12345678

Note: The numbers' length is variable.

I have tried casting numbers to string to measure their length and then divide them accordingly but there must be a more efficient and fast way than this.

are you sure that your current approach is too slow for your case? Or this question is just about interest of what are the ways to accomplish the task? — Alexander Manekovskiy, Jun 08 '14 at 17:06
@AlexanderManekovskiy I am performing this operation to a few million numerical pairs and it takes quite a while, I suppose it could go faster. — Doug Peters, Jun 08 '14 at 17:09

spender · Answer 1 · 2014-06-08T17:07:58.187

4

var left = 12345;
var right = 12345678;
var total = left + (right / Math.Pow(10, Math.Floor(Math.Log10(right)) + 1));

edited Jun 08 '14 at 17:07

answered Jun 08 '14 at 16:59

spender

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Thanks for the answer, however your solution fails when `right` is zero. – Doug Peters Jun 08 '14 at 17:35
@DougPeters : I think you'll need to special-case the zero value. – spender Jun 08 '14 at 23:15

score 3 · Accepted Answer · answered Jun 08 '14 at 17:04

3

A very quick and dirty approach, with no error checking at all

var total = Double.Parse(string.Concat(left, ",", right));

answered Jun 08 '14 at 17:04

Code Uniquely

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score 2 · Answer 3 · edited May 23 '17 at 10:32

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Based on https://stackoverflow.com/a/2506541/1803777, more performance can be obtained without usage of logarithm function.

public static decimal GetDivider(int i)
{
    if (i < 10) return 10m;
    if (i < 100) return 100m;
    if (i < 1000) return 1000m;
    if (i < 10000) return 10000m;
    if (i < 100000) return 100000m;
    if (i < 1000000) return 1000000m;
    if (i < 10000000) return 10000000m;
    if (i < 100000000) return 100000000m;
    if (i < 1000000000) return 1000000000m;
    throw new ArgumentOutOfRangeException();
}

int a = 12345;
int b = 12345678;
decimal x = a + b / GetDivider(b);

edited May 23 '17 at 10:32

Community

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answered Jun 08 '14 at 17:19

Ulugbek Umirov

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How does this scale so as to include BigInteger ranges as well? I wouldn't want to write a few hundred `if` lines. Any ideas? – Doug Peters Jun 08 '14 at 18:26
@DougPeters What type do you plan to use for that number of digits after the decimal? Technically you can make while loop to calculate the divider. – Ulugbek Umirov Jun 08 '14 at 18:41

score 1 · Answer 4 · edited May 23 '17 at 12:10

1

try counting using the following:

Math.Floor(Math.Log10(n) + 1);

then continue just as you stated.

Source: How can I get a count of the total number of digits in a number?

edited May 23 '17 at 12:10

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answered Jun 08 '14 at 17:12

vvvlad

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Attach decimal part to an integer

4 Answers4